The magnetic disk apparatus has a magnetic disk that is an information recording medium and a magnetic head to read and write magnetic information from and to the magnetic disk and includes a VCM actuator to support the magnetic head and move the magnetic head to a predetermined radial position over the magnetic disk. The magnetic information is written along a track circularly arranged on the magnetic disk. To correctly read and write the magnetic information, the magnetic head is required to be accurately positioned with respect to the track, so that, as the recording capacity and the recording density of the magnetic disk apparatus increase, a mechanism and a control method to achieve a higher positioning accuracy are required. One of the factors that degrade the positioning accuracy is the flow-induced vibration of the magnetic disk, which is called a disk flutter.
When the magnetic disk rotates, a complex air flow occurs in the magnetic disk apparatus. In particular, a high-speed and turbulent flow occurs around the magnetic disk, so that the disk flutter that is a vibration of the magnetic disk occurs due to pressure variation on the surface of the magnetic disk generated by the high-speed and turbulent flow. The disk flutter varies the position of the track to be followed by the magnetic head and degrades the positioning accuracy, so that reduction of the disk flutter is an important challenge to increase the recording density of the magnetic disk apparatus.
As one of the methods to reduce the disk flutter, a method for narrowing a gap between the magnetic disk and a shroud that covers the outer circumference of the magnetic disk, which is described in Patent Literature 1, and a method for inserting a partition member with a triangle cross section between disks, which is described in Patent Literature 2, are proposed. These methods suppress the turbulence of the air flow and reduce the disk flutter by stabilizing the flow around the magnetic disk by the shroud and the partition member. Further, as described in Patent Literature 3, a method for reducing the disk flutter by blowing air to the inner circumference of the disk is also known.